I give DD cows milk on all her things. If he is happy then that's your guide

I am not sure of the fat content difference between formula and full fat cows milk?
I still think you probably could drop even the day time bottle and see if that helps. Offer him water through the day, leave it around on the floor so he can get it if he wants.
It sounds like he is filling up on milk. The other thing to consider is how active he is. If he is crawling around and walking around furniture, then he will not gain alot of weight as he is active.
Good luck curly173.